Lasers Applications in Science and Industry Part 5 pdf

Effect of Pulse Laser Duration and Shape on PLD Thin Films Morphology and Structure 71 Gyorgy, E., Teodorescu, V.S., Mihailescu, I.N., Klini, A., Zorba, V., Manousaki, A., Fotakis, C. (2004) Surface Morphology Studies of Sub-Ps Pulsed-Laser-Deposited AlN Thin Film Journal of Materials Research volume 19, no. 3 (March 2004) pp 820-826, ISSN 2044-5326 Hergenroder, R., Miclea, M., Hommes, V., (2006) Controlling semiconductor nanoparticle size distributions with tailored ultrashort pulses Nanotechnology volume 17, no. 16 (August 2006) pp 4065-4071, ISSN 1361-6528 http://www.nasatech.com/Briefs/Feb04/LEW17186.html Hu, Z., Singha, S., Liu, Y., Gordon, R.J. (2007) Mechanism for the ablation of Si(111) with pairs of ultrashort laser pulses Applied Physics Letters volume 90, no. 13 (March 2007) pp 131910_1-3, ISSN 1077-3118 Itina, T. E., Shcheblanov, N. (2010) Electronic excitation in femtosecond laser interactions with wide-band-gap materials Applied Physics A: Materials Science & Processing volume 98, no. 4 (March 2010) pp 769–775, ISSN 1432-0630 Jegenyes, N., Toth, Z., Hopp, B., Klebniczki, J., Bor, Z., Fotakis, C. (2006) Femtosecond pulsed laser deposition of diamond-like carbon film: The effect of double laser pulses Applied Surface Science volume 252, no. 13 (April 2006) pp 4667-4671, ISSN 0169-4332 Judson, R.S., Rabitz, H. (1992) Teaching lasers to control molecules Physical Review Letters volume 68, no. 10 (March 1992) pp 1500-1503, ISSN 1079-7114 Kaganov, M. I., Lifshitz, I. M., Tanatarov, L. V. (1957) Relaxation between electrons and the crystalline lattice Soviet Physics – JETP volume 4 (1957) pp 173-180, ISSN 0038-5646 Klini, A., Loukakos, P.A., Gray, D., Manousaki, A., Fotakis, C. (2008) Laser Induced Forward Transfer of metals by temporally shaped femtosecond laser pulses Optics Express Vol. 16, No. 15 (July 2008) pp 11300-11309, ISSN 1094-4087 Lozovoy, V.V., Xu, B., Coello, Y., Dantus, M. (2008) Theoretical development of a high- resolution differential-interference-contrast optic for x-ray microscopy Optics Express volume 16, no. 2 (January 2008) pp 592-597, ISSN 1094-4087 Luculescu, C.R., Miyake, H., Sato, S. (2002) Deposition of BN thin films onto Si(1 0 0) substrate by PLD with nanosecond and femtosecond pulses in nitrogen gas background Applied Surface Science volume 197–198 (September 2002) pp 499–504, ISSN 0169-4332 Mihailescu, I.N., Hermann, J. (2010) Laser Plasma Interactions Laser Processing of Materials: Fundamentals, Applications, and Developments, Ed. P. Schaaf, pp 51–90, Springer Series in Materials Science, ISBN 978-3-642-13280-3, Springer Heidelberg Dordrecht London New York Miller, J.C. (Ed.) (1994) Laser Ablation Principles and Applications, Springer-Verlag, ISBN 3540575715 9783540575719 Berlin Miller, J. C., Haglund, R.F. (Eds.) (1998) Laser Ablation and Desorption, Academic Press, ISBN 0124759750 9780124759756, San Diego Millon, E., Albert, O., Loulergue, J. C., Etchepare, J. C., Hullin, D., Seiler, W., Perriere, J. (2000) Growth of heteroepitaxial ZnO thin films by femtosecond pulsed-laser deposition Journal of Applied Physics volume 88, no. 11 (December 2000) pp 6937- 6939; ISSN 1089-7550 Lasers – Applications in Science and Industry 72 Muller, G., Krotz, G., Niemann, E. (1994) SiC for sensors and high-temperature electronics Sensors and Actuators A: Physical volume 43, no. 1-3 (May 1994) pp 259-268, ISSN 0924-4247 Okoshi, M., Higashikawa, K., Hanabusa, M. (2000) Pulsed laser deposition of ZnO thin films using a femtosecond laser Applied Surface Science volume 154–155 (February 2000) pp 424-427, ISSN 0169-4332 Palmour, J. W., Edmond, J.A., Kong, H. S., Carter Jr., C.H. (1993) 6H-silicon carbide devices and applications Physica B: Condensed Matter volume 185, no 1-4 (April 1993) pp 461-465, ISSN 0921-4526 Papastathopoulos, E., Strehle, M., Gerber, G. (2005) Optimal control of femtosecond multiphoton double ionization of atomic calcium Chemical Physics Letters volume 408, no. 1-3 (June 2005) pp 65-70, ISSN 0009-2614 Parker, D.S.N., Nunn, A.D.G., Minns, R.S., Fielding, H.H. (2009) Frequency doubling and Fourier domain shaping the output of a femtosecond optical parametric amplifier: easy access to tuneable femtosecond pulse shapes in the deep ultraviolet Applied Physics B: Lasers and Optics volume 94, no. 2 (February 2009) pp 181–186, ISSN 1432- 0649 Perriere, J., Millon, E. Seiler, W. Boulmer-Leborgne, C. Craciun, V. Albert, O. Loulergue, J.C. Etchepare, J. (2002) Comparison between ZnO films grown by femtosecond and nanosecond laser ablation Journal of Applied Physics volume 91, no. 2 (January 2002) pp 690 - 696, ISSN 1089-7550 Piñon, V., Fotakis, C., Nicolas, G., Anglos, D. (2008) Double pulse laser-induced breakdown spectroscopy with femtosecond laser pulses Spectrochimica Acta Part B: Atomic Spectroscopy volume 63, no. 10 (October 2008) pp 1006-1010; ISSN 0584-8547 Pronko, P.P., Cutta, S.K., Squier, J., Rudd, J.V., Du, D., Mourou, G. (1995) Machining of sub- micron holes using a femtosecond laser at 800 nm Optics Communications volume 114, no. 1-2 (January 1995) pp 106–110, ISSN 0030-4018 Pronko, P.P., Zhang, Z., Van Rompay, P.A. (2003) Critical density effects in femtosecond ablation plasmas and consequences for high intensity pulsed laser deposition Applied Surface Science volume 208–209 (March 2003) pp 492-501, ISSN 0169-4332 Qian, F., Craciun, V., Singh, R.K., Dutta, S.D., Pronko, P.P. (1999) High intensity femtosecond laser deposition of diamond-like carbon thin films Journal of Applied Physics volume 86, no. 4 (August 1999) pp 2281-2290, ISSN 1089-7550 Ristoscu, C., Mihailescu, I.N., Velegrakis, M., Massaouti, M., Klini, A., Fotakis, C. (2003) Optical Emission Spectroscopy and Time-of-Flight investigations of plasmas generated from AlN targets in cases of Pulsed Laser Deposition with sub-ps and ns Ultra Violet laser pulses Journal of Applied Physics volume 93, no. 5 (March 2003) pp 2244-2250, ISSN 1089-7550 Ristoscu, C. Gyorgy, E. Mihailescu, I. N. Klini, A. Zorba, V. Fotakis, C. (2004) Effects of pulse laser duration and ambient nitrogen pressure in PLD of AlN Applied Physics A: Materials Science & Processing volume 79, no 4-6 (September 2004) 927-929 ISSN 1432-0630 Ristoscu, C., Socol, G., Ghica, C., Mihailescu, I.N., Gray, D., Klini, A., Manousaki, A., Anglos, D., Fotakis, C. (2006) Femtosecond pulse shaping for phase and morphology control in PLD: Synthesis of cubic SiC Applied Surface Science volume 252, no 13 (April 2006) pp 4857-4862, ISSN 0169-4332 Effect of Pulse Laser Duration and Shape on PLD Thin Films Morphology and Structure 73 Schmidt, B., Hacker, M., Stobrawa, G., Feurer, T. (n.d.) LAB2-A virtual femtosecond laser lab Available from http://www.lab2.de Sheng, S., Spencer, M.G., Tang, X., Zhou, P., Wongchoitgul, W., Taylor, C., Harris, G. L. (1997) An investigation of 3C-SiC photoconductive power switching devices Materials Science and Engineering B volume 46, no. 1-3 (April 1997) pp 147–151, ISSN 0921-5107 Singha, S., Hu, Z., Gordon, R.J. (2008) Ablation and plasma emission produced by dual femtosecond laser pulses Journal of Applied Physics volume 104, no. 11 (December 2008) pp 113520_1-10, ISSN 1089-7550 Stoian, R., Boyle, M., Thoss, A., Rosenfeld, A., Korn, G., Hertel, I. V., Campbell, E. E. B. (2002) Laser ablation of dielectrics with temporally shaped femtosecond pulses Applied Physics Letters volume 80, no. 3 (January 2002) pp 353-355, ISSN 1077-3118 Stoian, R., Boyle, M., Thoss, A., Rosenfeld, A., Korn, G., Hertel, I. V. (2003) Dynamic temporal pulse shaping in advanced ultrafast laser material processing Applied Physics A: Materials Science & Processing volume 77, no. 2 (July 2003) pp 265-269, ISSN 1432-0630 Tanabe, T., Kannari, F., Korte, F., Koch, J., Chichkov, B. (2005) Influence of spatiotemporal coupling induced by an ultrashort laser pulse shaper on a focused beam profile Applied Optics volume 44, no. 6 (February 2005) pp 1092-1098, ISSN 2155-3165 Teghil, R., D’Alessio, L., Santagata, A., Zaccagnino, M., Ferro, D., Sordelet, D.J. (2003) Picosecond and femtosecond pulsed laser ablation and deposition of quasicrystals Applied Surface Science volume 210, no. 3-4 (April 2003) pp 307-317, ISSN 0169-4332 Trebino, R., Kane, D.J. (1993) Using phase retrieval to measure the intensity and phase of ultrashort pulses: frequency-resolved optical gating Journal of the Optical Society of America A volume 10, no. 5 (May 1993) pp 1101–1111, ISSN 1520-8532 Trebino, R., DeLong, K.W., Fittinghoff, D.N., Sweetser, J.N., Krumbügel, M.A., Richman, B.A., Kane, D.J. (1997) Measuring ultrashort laser pulses in the time-frequency domain using frequency-resolved optical gating Review of Scientific Instruments volume 68, no. 9 (September 1997) pp 3277-3295, ISSN 1089-7623 Trebino, R. (2002) Frequency-Resolved Optical Gating: The Measurement of Ultrashort Laser Pulses Kluwer Academic ISBN 1402070667 9781402070662, Boston Verluise, F., Laude, V., Cheng, Z., Spielmann, C.H., Tournois, P. (2000) Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping Optics Letters volume 25, no. 8 (April 2000) pp 575-577, ISSN 1539-4794 Von Allmen, M., Blatter, A. (1995) Laser-Beam Interactions with Materials (2nd edition) Springer, ISBN 3540594019 9783540594017, Berlin; Heidelberg; New York; Barcelona; Budapest; Hong Kong; London; Milan; Paris; Tokyo Wefers, M.M., Nelson, K.A. (1995) Analysis of programmable ultrashort waveform generation using liquid crystal spatial light modulators Journal of the Optical Society of America B volume 12, no. 7 (July 1995) pp 1343-1362, ISSN 1520-8540 Weiner, A. M. (2000) Femtosecond pulse shaping using spatial light modulators Review of Scientific Instruments volume 71, no. 5 (May 2000) pp 1929-1960, ISSN 1089-7623 Zhang, Z., VanRompay, P.A., Nees, J.A., Clarke, R., Pan, X., Pronko, P.P. (2000) Nitride film deposition by femtosecond and nanosecond laser ablation in low-pressure nitrogen Lasers – Applications in Science and Industry 74 discharge gas Applied Surface Science volume 154–155 (February 2000) pp 165–171, ISSN 0169-4332 Zhigilei, L. V., Garrison, B. J. (2000) Microscopic mechanisms of laser ablation of organic solids in the thermal and stress confinement irradiation regimes Journal of Applied Physics volume 88, no. 3 (2000) pp 1281-1298, ISSN 1089-7550 4 Laser Pulse Patterning on Phase Change Thin Films Jingsong Wei 1 and Mufei Xiao 2 1 Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences 2 Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México 1 China 2 México 1. Introduction In the present chapter, we discuss the formation of microscopic patterns on phase change thin films with low power laser pulses. The discussions are mostly based on our recent experimental and theoretical results on the subject. Phase change thin films are widely used as optical and electric data storage media. The recording is based on the phase change between the crystalline and amorphous states. In the writing process, a small volume in the thin film is locally and rapidly heated to above the melting point and successively quenched into the amorphous phase. In the erasing process, the material undergoes a relatively long heating to reach a temperature above the glass transition but yet below the melting point, which brings the material back to the crystalline phase. However, during the writing process, apart from the phase changes, physical deformation of the surface occurs, which often creates bumps of various forms. In other words, low intensity laser pulses are able to microscopically form patterns on phase change films. The formed patterns modify the topographic landscape of the surface and bring about variations on the material properties of the films. The modifications can be harmful or helpful depending on what kind of applications one looks for. Therefore, in order to properly deal with the laser induced bumps, it is essential to understand the process of bump formation, and to qualitatively and quantitatively describe the created bumps as well as its relation with the laser pulse parameters, such as the beam distributions and the average intensity etc. so that one is able to closely control the formation of microscopic patterns on phase change films with low power laser pulses. Recently, we have systematically studied the formation of bumps during laser writing both experimentally and theoretically. In the present chapter we shall round up the important results from our studies and present detailed discussions on the results. We organize the chapter as follows. In the first part, we present results of forming circular bumps as a by-production of rather conventional laser writing process for the purpose of data storage on Ag 8 In 14 Sb 55 Te 23 chalcogenide phase change films. In this part, the detailed process of writing and erasing will be described, and Lasers – Applications in Science and Industry 76 the experimental and theoretical characterizations of the bumps are demonstrated. In the second part, we expand our work to intentionally form micro patterns on multilayer ZnS– SiO 2 /AgO x /ZnS–SiO 2 thin films by laser direct writing technology. We shall conclude the work in the end of the chapter. 2. Laser pulse induced bumps in chalcogenide phase change films Chalcogenide phase change thin films are widely used as optical and electric data storage media. The recording is based on the phase change between the crystalline and amorphous states (Kolobov et al., 2004; Kalb et al., 2004; Welnic et al., 2006; Wuttig & Steimer, 2007). In the writing process, a small volume in the thin film is locally and rapidly heated to above the melting point and successively quenched into the amorphous phase. In the erasing process, the material undergoes a relatively long heating to reach a temperature above the glass transition but yet below the melting point, which brings the material back to the crystalline phase. The heat source for the phase change is usually from laser pulses in optical data storage, or electric current pulses in electric data storage. In the present work we shall selectively concentrate on the optical storage. In the process of amorphization, i.e., the laser writing process, the material experiences a volume change due to the stronger thermal expansion in the melting state than in the crystalline state, as well as the density difference between the two states. Therefore, the amorphous recording marks are actually physically deformed as circular bumps because the amorphous recording marks inherit the volume in the melting state after a fast cooling stage. Subsequently, the bumps may cause further deformation in other thin layers stacked underneath as in the cases of optical information memory in optical storage and the electrode in electric storage. While slight deformation in the writing process is inevitable, significant bumps are harmful for the storage media as they affect dramatically the size of the marks, which eventually reduces the recording density of the media, and shorten the durability of the device. In extreme cases the bumps may grow so big that a hole is formed at the apex of the bump. Therefore, to quantitatively describe the bump formation is of great interest for storage applications. We have established a theoretical model for the formation process, where the geometric characters of the formed bumps can be analytically and quantitatively evaluated from various parameters involved in the formation. Simulations based on the analytic solution are carried out taking Ag 8 In 14 Sb 55 Te 23 as an example (Wei et al., 2008; Dun et al., 2010). The results are verified with experimental observations of the bumps. 2.1 Theory Let us start by describing the amorphization process schematically in the volume- temperature diagram as shown in Fig. 1, where the principal paths for the phase changes are depicted. Initially, the chalcogenide thin film is considered in the crystalline state represented by point a; a laser or current pulse of nanosecond duration heats the material up to the melting state, which is represented by point b. Subsequently, the material is cooled quickly with a high rate exceeding 7 10 /Cs to the room temperature to form the final amorphous mark. During the quenching stage, the material structure does not have sufficient time to rearrange itself and remains in the equilibrium state, and thus inherits the structure and volume at the melting state. Therefore, the volume has an increase V , and Laser Pulse Patterning on Phase Change Thin Films 77 the mark appears as a bump. If the laser or current pulse injects energy higher than the ablated threshold corresponding to the vaporization temperature, the heating temperature reaches point d, and the material is then rapidly cooled to the room temperature, which is represented by point e; an ablated hole can be formed at the top of the bump. Fig. 1. Volume-temperature diagram of chalcogenide films. The film is heated by laser from point a to point b and returns to point d, or to point c and returns to point e after faster cooling. The geometric characters of the bump are graphed in Fig. 2, where cross-sections of the circular bump are schematically shown respectively for the case of a bump and the case of a bump with a hole on its top. It is worth noting that, in general, the volume thermal expansion coefficient for chalcogenide thin films has two different constant values in the crystalline and melting states, respectively. In our analysis, there is assumed a Gaussian intensity profile for the incident laser pulse, and volume changes occur only in the region irradiated by the laser pulse, as shown in Fig. 2(a). If the laser pulse energy exceeds the ablated threshold, a hole is to be formed at the top of the bump, which is shown in Fig. 2(b). Mathematically, for the fast heating and amorphization process, the net volume increase can be written as 0 ()( ) mc sur f m hVTT        , where m  and c  are the volume thermal expansion coefficients in the crystalline and melting states, respectively. 0 V is the irradiated region volume. T surf is the material surface temperature heated by laser pulse and m T is the temperature corresponding to the melting point. Since the irradiated region is axially symmetric due to the Gaussian laser beam intensity profile, the bump height can be expressed as )()()()( 0 msurfcm TTrhrh         (1) where r is the radial coordinate, and 0 ()hr is the height of the irradiated region. Lasers – Applications in Science and Industry 78 Fig. 2. Bump formation schematics: (a) bump and (b) hole on the top of bump. Furthermore, the absorbed energy per unit volume and per unit time can be calculated by 2 22 22 (,) (1 ) exp( )exp( ) Pr grz R z ww      (2) where  is the absorption coefficient, R is the reflectivity of the material, P is the laser power, w is the laser beam radius at the 2 1/e of the peak intensity, and z is in the depth direction from the sample surface. In Eq. (2) the quantity  1 R   is the absorbed part of the transmitted light, which decays exponentially  exp z   along the z direction and spreads as a Gaussian function  22 exp 2 /rw in the r direction. Generally for data storage, the width of the laser pulse is in the range from nanosecond to millisecond. Within this range, the temperature distribution in the irradiated region can be expressed as (,) (,) p grz Trz C    (3) where  is the density, p C is the heat capacity of the material, and  is the laser pulse width. According to (Shiu et al., 1999), the bump height ()hr can be calculated, within the Laser Pulse Patterning on Phase Change Thin Films 79 temperature interval   ,0 m f TTr T   , where f T is the temperature corresponding to the vaporization point above which the material will be ablated, by  (,0) () (,0) ln mc m m Tr hr Tr T T            (4) and the bump diameter p d can be calculated by setting   ,0 m Tr T and /2 p rd  in Eq. (3) with  0 1 1 2ln p p m R dwF CT         (5) where 2 0 2/FPw   . Similar to the derivation of bump diameter, if the laser pulse energy exceeds the ablated threshold, an ablated hole is formed when   ,0 f Tr T and the hole diameter in the bump hole d can be calculated as  0 1 1 2ln hole pf R dwF CT             (6) It should be noted that in our analytical model, the thermo-physical parameters of material are assumed independent from temperature. 2.2 Experimental observations Before presenting results of simulation based on the above developed formalism, let us show some experimental observations of the bumps. The experimental results provided useful and meaningful values for choosing the parameters involved in the theoretical simulations. In the experiments, Ag 8 In 14 Sb 55 Te 23 thin films were directly deposited on a glass substrate by dc-magnetron sputtering of an Ag 8 In 14 Sb 55 Te 23 target. The light source is a semiconductor laser of wavelength 650nm   , and the laser beam is modulated to yield a 50ns laser pulse. The laser beam is focused onto the Ag 8 In 14 Sb 55 Te 23 thin film, and the light spot diameter is about 2 m  . In order to form bumps with different sizes, various laser power levels were adapted. Some of the experimental results are presented in Figs. 3–5. Fig. 3(a) shows some bumps obtained with laser power 3.8mW . The inset in Fig. 3(a) is an enlarged image of one bump. The bump diameter is about 0.9 1.0 m   . In order to further analyze the bump morphology, an atomic force microscope (AFM) was used to scale the bump. The results are shown in Fig. 3(b), where the top-left inset shows the same bumps as in Fig. 3(a), and the top-right inset is the cross-section profile of the bump. One notes that the bump height is about 60 70nm , and the diameter is about 1 m  . With the increase of laser power, a round hole in the bump is formed, as shown in Fig. 4, where the laser powers are 3.85 , 3.90, and 4.0 mW, respectively. The corresponding bumps are shown from left to right in Fig. 4. The bumps in Fig. 5(a) were produced at laser power level 4.0 mW. In Fig. 5(a) the left- bottom inset is an enlarged bump image. It is found that holes are formed in the central region of the bumps. Fig. 5(b) presents the AFM analysis, where the top-right inset is the three-dimensional bump image. It can be seen that the bump diameter is about 1 m  , and the size of the hole is about 250 300nm  . Lasers – Applications in Science and Industry 80 Fig. 3. Bumps formed at laser power 3.8mW : (a) SEM analysis and (b) AFM analysis. Fig. 4. SEM analysis for bumps formed at laser power of 3.85 , 3.90 and 4.0mW . [...]... calculations were obtained from experiments The melting and vaporization points of Ag 8In1 4Sb55Te23 were measured by a differential scanning calorimeter (DSC), and the results are given in Fig 6 It can be seen that the 82 Lasers – Applications in Science and Industry melting Tm and vaporization T f points are 51 2 °C and 738 °C, respectively It should be noted that T f is determined by the cross point between... structures appear taper shape and are very regular and uniform The boundary between the area with and without laser irradiation is well defined, and the patterns are very uniform and smooth 88 Lasers – Applications in Science and Industry We also chose six pattern units (marked by line in Fig 13(b)) to measure the height and diameter of the structures, and the result is shown in Fig 13(c) One notes that... (b) 3D image of bump, and (c) top-view of bump 83 84 Lasers – Applications in Science and Industry Fig 8 Simulation results for laser power 4.0mW : (a) temperature profile and (b) hole formed at the top of bump Laser Pulse Patterning on Phase Change Thin Films 85 With an increase of laser power, the temperature of thin films will exceed the vaporization point, and the ablation in the bump will take... between the tangent lines of AB and CD The capacity C P was also measured to be about 320 J / KgK by the DSC method The density is obtained by    Ag  8  m  14  Sb  55  Te  23 / 100  6981.2Kg / m2 The thermophysical parameters used in the calculation are listed in Table I The volume thermal expansion coefficients of Ag 8In1 4Sb55Te23 thin film in the crystalline and melting states are difficult... not need developing and etching process, and the laser power is required to be in a very low range, so it is suitable to fabricate a large-area pattern structure in very short time and very low cost, which largely decrease the time-consuming and industrial cost 3.1 Principle It is well known that in an open system the AgOx material is chemically known to decompose into Ag particles and O2 at about... measure, and we estimated that c and  m were 25  10 6 / °C and 25  10 3 / °C, respectively This is reasonable because the linear thermal expansion coefficient in liquid state is about ten times that in the solid state, therefore, the corresponding volume thermal expansion coefficient in the liquid state is about 10 3 times that in the solid state   Fig 6 DSC analysis for Ag 8In1 4Sb55Te23 thin films... decompose to Ag and O2 according to AgOx →Ag+x2O2 The decomposition reaction has been verified by many methods When the laser beam irradiates on the AgOx film, a small volume of thin film is locally and rapidly 86 Lasers – Applications in Science and Industry heated to above the decomposing temperature, and then the reaction happens The oxygen released by the decomposition is stayed in the enclosed... decomposes into silver and oxygen The O2 and Ag particles are rough and tumble and filled the whole room After the AgOx cooling down to the room temperature, the expanded volume will be left as bump If we precisely control the laser parameters, the regular and uniform bump array pattern structure can be obtained Fig 9 Schematic of laser direct writing multilayered AgOx thin film (a) Laser irradiated the thin... established model and the developed formalism 3 Patterning on multilayer thin films with laser writing Recently, pattern structures have been used widely in many fields, such as photonic crystal and solar cell industry, owing to its advantages over the common coatings In the last several years, pattern structures have been fabricated on silicon, quartz, and especially photo-resist by many kinds of technologies,... better performance In this work, we find that the aspect ratios rapidly increase from the minimum of 0.012 at laser power of 3.0 mW to the maximum of 0.201 at laser power of 5. 0 mW, which indicates that the better aspect ratio can be obtained in higher laser powers In order to obtain more details about the pattern structure, we amplify a small area from Fig 11(a), and the result is shown in Fig 13(a) It . Principles and Applications, Springer-Verlag, ISBN 354 057 57 15 978 354 057 5719 Berlin Miller, J. C., Haglund, R.F. (Eds.) (1998) Laser Ablation and Desorption, Academic Press, ISBN 0124 759 750 . femtosecond and nanosecond laser ablation in low-pressure nitrogen Lasers – Applications in Science and Industry 74 discharge gas Applied Surface Science volume 154 – 155 (February 2000) pp 1 65 171,. phase change films. In this part, the detailed process of writing and erasing will be described, and Lasers – Applications in Science and Industry 76 the experimental and theoretical characterizations